From the Super Mario Wiki
Wrinkly's Retreat is an shrine where Wrinkly Kong resides in the Game Boy Advance remake of Donkey Kong Country 3: Dixie Kong's Double Trouble! It is where Wrinkly looks after the Banana Birds that were rescued by Dixie and Kiddy Kong. Wrinkly's Retreat replaces Wrinkly's Save Cave from the original version, as the player can save their game from the world map at any time. There is only one Wrinkly's Retreat, located in the main Northern Kremisphere map between Bazaar's General Store and Funky's Rentals. The rest of the Save Caves were replaced with Cranky's Dojo.
Unlike her Save Cave, Wrinkly does not do much else, such as exercising, sleeping, or playing the Nintendo 64, although she does keep track of the Kongs' progress. The interior of Wrinkly's Retreat shows the pattern from the Queen Banana Bird's barrier on three sides of the wall and a small pool of water in the center. Each Banana Bird that the Kongs have rescued are shown moving around the place.
After obtaining every Banana Bird then returning to Wrinkly's Retreat, the Banana Birds fly out of Wrinkly's Retreat and carry the Kongs up with them to the Queen Banana Bird. This triggers a secret ending involving the Queen getting her revenge on Baron K. Roolenstein.